1. Field of the Invention
The present invention generally relates to a mounting construction and method of a semiconductor device, and more particularly to a mounting construction and method of a semiconductor device which is mounted to a mounting board, and a lead frame used in the mounting construction.
In recent years, semiconductors have become highly integrated, and at the same time a miniaturization of the semiconductor devices is required. In order to satisfy those requirements, a lead pitch of leads extending from a package of a semiconductor device has become extremely narrow.
If the lead pitch is reduced, strength of the leads is also reduced. Accordingly there is a possibility that the leads are deformed due to an external force during delivery, and thus reliability of the semiconductor device is decreased. Additionally, when the semiconductor device having a narrow lead pitch (fine pitch) is directly mounted onto a mounting board, a so-called bridging in which a solder bridges over adjacent leads may occur, and thus mountability of the semiconductor device is deteriorated.
Accordingly, it is desirous to develop a mounting construction and method of a semiconductor device through which a deformation of leads can be prevented, and good mountability is achieved.
2. Description of the Related Art
As a method of preventing a deformation of the leads of the semiconductor device having leads with a fine pitch, the mold carrier ring (MCR) method is known. A semiconductor device manufactured by the MCR method has a construction in which extreme ends of leads extending from a semiconductor package are molded into a frame member (ring-like member) so that the leads are maintained at a predetermined distance away from each other.
FIG. 1 is a plan view of a conventional semiconductor device manufactured by the MCR method. As shown in FIG. 1, the semiconductor device 1 manufactured by the MCR method comprises a semiconductor package 2 and a ring member 3. The semiconductor device 1 is delivered from a manufacturing plant in a state in which the ring member 3 is not separated from the semiconductor package 2.
The semiconductor package 2 has a plastic package 4 in which a semiconductor chip (not shown in the figure) is sealed, a plurality of leads 5 extending from outer sides of the plastic package 4. The ring member 3 is a frame-like member which encircles the semiconductor package 2, and is also formed of a plastic.
Extreme ends of the leads 5 extending from the plastic package 4 are molded in the ring member 3, and thereby the semiconductor package 2 is retained inside the ring member 3. Accordingly, the leads 5 are protected from an external force, and thus deformation of the leads 5 is prevented. Therefore, the leads 5 can be arranged with fine pitches without having a short circuit between adjacent leads, and flatness of the leads 5 can be well maintained.
As mentioned above, the semiconductor device 1 manufactured by the MCR method has the ring member 3 which protects the lead 5 from being deformed, the ring member 3 being provided only to protect the leads 5 from being deformed. Since the semiconductor device 1 is delivered in a state in which the ring member 3 is still attached to the leads 5, the ring member 3 must be removed from the semiconductor package 2 at a user's site where the semiconductor package 2 is assembled in a product.
Accordingly, a lead cutting apparatus to remove the ring member 3 from the semiconductor package 2 must be installed at the user's site, the lead cutting apparatus cutting off the leads 5 at predetermined positions thereof. Since the lead cutting apparatus is required to cut off the leads while maintaining the lead pitch of the leads 5 and preventing a deformation of the leads 5, a high technique is required for manufacturing the lead cutting apparatus. Accordingly, the lead cutting apparatus is expensive, and thus it is not practical to install the lead cutting apparatus at each user's site.
Additionally, after the ring member 3 is removed from the semiconductor package 2, no protection is provided on the leads 5. Therefore, there still be a problem in that the leads 5 are deformed and short circuited during a mounting process of the semiconductor package 2 on to a mounting board. Further, since the leads 5 are arranged with the fine pitch, there still be a problem in that a solder bridge is formed between the adjacent leads 5, resulting in deterioration of mountability.
In the mounting process of the semiconductor package 2, the leads 5 and electrodes formed on a mounting board are soldered by melting solder provided on lead connecting portions after the semiconductor package 2 is placed directly on the mounting board. Accordingly, heat is applied inevitably to the semiconductor package 2 during a mounting process. In such a condition, a heat stress may be generated in the plastic package 4, and thus there is a problem that a crack may be generated in the plastic package 2.